Metallocene complexes of Group 4 from the Periodic Table have been widely used as precursors of catalysts for olefin polymerization. The substitution of the cyclopentadienyl ligands used in these metallocenes is widely recognized to play a critical role in determining the catalyst system's polymerization activity and selectivity. It is also well known that if two cyclopentadienyl ligands are bridged by a common substituent such as a dihydrocarbyl silyl group. The catalysts properties can change dramatically relative to the non-silyl bridged analogue.
For example, the unbridged (2-methylindenyl)ZrCl2/MAO (MAO=methylalumoxane) is a poor catalyst system for isotactic polypropylene production, while in contrast, rac-Me2Si(2-methylindenyl)2ZrCl2/MAO polymerizes propylene to a highly isotactic polymer. Also, an increase in molecular weight can be observed by a simple change in bridging group. For instance, a 23% increase in molecular weight for ethylene polymerization was observed upon changing the bridging group from Me2Si in Me2Si(indenyl)2ZrCl2/MAO to Ph2Si in Ph2Si(indenyl)2ZrCl2/MAO in 193 Makromol. Chem. 1643 (1992), and EP 0399348A2.
The Ph2Si(indene)2 ligand was prepared from Ph2SiCl2 and two equivalents of indenyl lithium in only 42% yield, as disclosed in EP 0376154, herein incorporated by reference for purposes of U.S. patent practice. The preparation of the metallocene Ph2Si(2-methylindenyl)2 ZrCl2 from ZrCl4 and Ph2Si(2-methylindenyl lithium)2 has been reported but was without the procedure for preparing Ph2Si(2-methylindene)2, as in EP 485822A1, EP 485823A1, herein incorporated by reference for purposes of U.S. patent practice.
Silyl bridged metallocenes are typically prepared from reaction of organometallic cyclopentadienyl ligands and dihydrocarbylsilyldichlorides. There has also been an example of using dimethysilylditriflate as the silylating agent disclosed in WO 99/38871. However, the use of diarylsilylditriflates has not received similar scrutiny. These reagents are readily prepared from diarlysilyldichlorides and silver triflates or protonolysis of tetraarylsilanes with triflic acid discussed in 103 Chem. Ber. 868 (1970); 409 J. Organomet. Chem. 377 (1991). This invention encompasses the process of using diarylsilyldisulfonates to prepare diarylsilylbridged dicyclopentadienyl ligands and metallocenes containing diarylsilylbridged dicyclopentadienyl ligands and polymers prepared with metallocenes containing diarylsilylbridged dicyclopentadienyl ligands.